Have you seen the term Digestible Energy or DE used to describe the value of your horse feed? Do you understand why they use this term in horse nutrition? Well, if you aren’t quite sure join the club! Many of my nutrition consults include an explanation of this concept.

Even though Digestible Energy (DE) is the most common method for measuring horse feed most horse owners still rely on the basics percentages of protein, fat & fiber to decide on what diet they feed. It’s really not that hard to understand if you keep it simple.

There are two concepts you need to look at; Energy and Digestibility.

Energy basically equals Calories. Yes, with a capital C, the little c is for human food and too small to use with horses. A capital C calorie is also called a kilocalorie. Wait, there’s more. Because horses use so many kilocalories energy requirements are expressed as megacalories (Mcal) in the nutrient requirement of horses. There are 1,000 kilocalories in a megacalorie. So 1 Mcal = 1 Calorie or kcal.

Gross Energy (GE) is the total energy value of a feed before accounting for energy losses due digestion, or metabolic and bodily functions. However, to be a good indicator of productive, or useful energy, the various losses of energy must be taken into account so GE isn’t the most accurate measure. So we look at what’s left.

The energy-producing component of a horse’s diet can be divided into three classes of nutrients: protein, fat, and carbohydrates. Gross energy for carbohydrates is 4.15 kcal/g; for fats, 9.40 kcal/g; and for proteins, 5.65 kcal/g.

The second concept we consider is Digestibility. Simply put Digestibility refers to the extent to which a feedstuff (grain, hay, grass) is absorbed in the animal’s body as it passes through the digestive tract. So basically what goes in minus what comes out.

To get Digestible Energy you measure (and they actually do) the total amount of Gross energy the horse took in (intake) and then measure the energy lost in the feces (and yes, that do that too). What you would be left with is the amount of energy that is assumed to be digested. DE calculations are tricky in horses because fecal energy (FE) only partially accounts for the energy loss, as I said before, energy is also lost in a horse’s urine and gas in the process.

To determine DE values researchers measure daily feed intake and total fecal output during a collection period. Subsamples of the daily feed type and feces are taken and frozen. Because moisture can influence the nutrient concentration of a sample these subsamples are dried. Then the samples are analyzed for dry matter, crude protein, ADF, NDF, crude fiber, fat, calcium, phosphorus, magnesium, potassium, zinc, copper, manganese, and ash.

Digestible Energy provides an estimate of the amount of energy from a feed that is available for the horse to use. DE is used to balance the energy portion of the equine diet so knowing the DE of your horse’s feedstuff is helpful when you are calculating a ration and developing your feeding program. DE is measured on a dry matter basis so you can compare things like wet grass and oil to dried hay and grains.

Certain factors like the composition of the food they eat, the way the food was processed, the amount of food in the diet, and the make-up of the diet (forage only or forage plus concentrate) can affect digestibility in horses.

But let’s not get ahead of ourselves. Before you need to develop a diet using DE values you must begin with an understanding of the amount of energy your particular horse needs to stay healthy and do the job asked of it.

Of course these are a general rule of thumb. There are other factors that influence energy needs. You should allow consideration for differences in:
• Management Conditions -stalls would have lower energy requirements versus paddocks where they move around a lot
•Temperament- easy keeper versus hard keeper
•Age- young would have an increased activity versus old with a decreased activity
• Breed- draft and pony breeds with lower requirements versus light horse breeds with greater requirements
•Sex- stallions might have an increased demand versus geldings and mares.

Once you determine how much DE your horse needs you then decide the best source of that energy in the various feedstuffs your horse can consume. There are multiple ways to determine DE and most require a laboratory.

Lab analysis uses different ways to determine DE content but I’m not going to get into each of them. The most common method to predict Digestible energy uses the chemical composition of the feeds (remember the researchers above?) and is described in the following equation recognized by the NRC 2007 (the “bible” of equine nutrition).

DE x (kcal/kg DM) = 2118 + 12.18 x (%CP) – 9.37 x (%ADF) – 3.83 x (%hemicellulose) + 47.18 x (%fat) + 20.35 x (%NSC) – 26.3 x (%ash)
Where hemicellulose = Acid Detergent Fiber (ADF) – Neutral Detergent Fiber (NDF) & Non Structural Carbohydrates (NSC) = (100 – %NDF – %Fat – %Ash – %CP).

Note: It has been found that this calculation does not accurately predict the DE content of some high fiber feeds and feeds that are high in fat.

You can stop frowning now. 🙂 You don’t need to get your calculator out because there are accepted ranges in DE values of some common feedstuff. You might have noticed that feed companies do not list the Mcal of DE on feed tags so to be absolutely certain of the DE values in your commercial grain you should contact your feed company. Unfortunately, there are no regulatory bodies telling equine feed manufactures which method or equation to use to estimate energy content of feed. This means companies can use whatever system they want to predict DE and this can potentially be very misleading to the end user. But here are some generally accepted values:

In my opinion all hay growers should be required to send a sample in and have it tested so you know what you are buying but most don’t. So to be certain of the DE of your hay you can easily send off your hay for DE analysis. But here again are some generally accepted DE values:

As you can see DE varies greatly with the type of feedstuff and type of animal concerned. Using the charts in this post lets calculate the amounts of DE needed for a quiet, 1,100 pound QH gelding kept in a field and in light work.

The basic Mcals/day for this size horse is 20. The fact that he is in a field could increase this number but given that he is quiet and a Quarter Horse I’d say that offsets the field boarding increase. So we will go with 20 Mcal/day or 20,000 kilocalories.

The owner of this horse buys mixed hay of decent quality and a commercial grain with a 4% fat. The range for commercial feeds is .09-1.8 Mcal/pound so we will say this moderate fat feed is 1.3 Mcal/pound.

As any regular reader knows The Nerd likes to see a horse on a forage based diet. So I would like it if the majority of this horse’s energy needs are met with his hay. At .90 Mcal/pound he would need to eat 22 pounds of hay a day to meet his needs. That’s almost a half a bale. Since it’s only average quality it probability has some lignin in it (the stemmy stuff that makes horses not like it) so that might be unrealistic.

You have two choices in this situation; get better quality hay or reduce the hay amount and add grain.

This owner isn’t switching hay so let’s calculate the same needs but with a 1.5% body weight in hay (16 pounds/day) and with .5% of BW in grain (5 ½ pounds/day) diet which might be easier to do.

16 pounds of his hay would have 13.6 Mcal (16 x .90 ) and his grain would have 7 Mcal (5.5 x 1.3 ) for a total of 20.6 Mcal/day in his diet, right on target.

In my opinion DE values are a great start but should not be the sole consideration when making decisions about what feed program is right for your horse. The actual source of the energy is a better indicator. For example, you should make sure the diet is based on fiber to maintain normal gut and digestive function and to limit the potential of behavioral problems. Make sure there are appropriate levels of soluble carbohydrates in the diet for your particular horse which will help maintain energy without overloading the digestive capacity of the horse or causing metabolic disturbances. Finally, if your horse needs extra energy there should be adequate fat in the diet to maintain the required energy without the need to overload the digestive tract with large amounts of feed.

In summary, the horse needs water, energy, vitamins and minerals to survive. Energy comes from the carbohydrates, fat and protein in their diets. Digestible Energy is a useful way to look at the energy values of the various feedstuffs in the equine diet. By comparing the digestibility of the things you feed your horse you can tweak your nutrition program to fit your horse’s needs easily.

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Peace and Good Feed,

~The Nerd